The exemplary embodiment relates to a buffering system for accommodating uncertainties in a media processing module, such as a marking engine. It finds particular application in a modular printing system in which various media processing modules are under the control of a common controller and will be described with particular reference thereto. However, it is to be appreciated that the present exemplary embodiment is also amenable to other like applications.
Printing systems, such as copiers, printers, and multifunction devices, generally include at least one marking engine for applying images to sheets of print media using marking materials, such as inks or toners. Modular integrated printing systems have been developed in which various components, such as sheet feeders, conveyors, marking engines, and finishers, are configured as interchangeable modules, allowing the printing system to be reconfigured or components removed for repair or replacement. To ensure that the various components operate in harmony and an optimum throughput is maintained, a central controller oversees the movement of the print media through each of the modules, allowing accurate timing of the print media. Model-based planning may be used to create machine control plans. This control method relies on the capability of each component of the system to send a model of its behavior to the central controller. The central controller interprets the models to determine the capabilities and constraints of the system components. When a print job is received for processing, the controller generates a plan to process one or more print jobs based on the components' capabilities and capability constraints described within each of the component models. The plan may then be confirmed by each component of the system to ensure that each component can execute its portion of the plan.
It would be advantageous to be able to incorporate, into such a modular printing system, one or more marking engines which have not been specifically designed to function entirely under the control of a central controller. One reason for this is to provide functionality not available in the modular marking engines, such as high speed printing. Another reason is to allow greater flexibility to a print shop in the way in which existing equipment is utilized. Marking engines which are not designed to operate in an integrated printing system have their own control unit, which controls the movement of the print media through the marking engine. Such control units are not programmed to provide detailed information on the capabilities and constraints of the marking engine to an external controller. Additionally, the marking engine control unit may determine when the device should go down for a short period to perform internal checks. This can result in uncertainties in the timing of the sheets, at least as far as the central controller is concerned.
Sheet buffers have been developed to temporarily hold or delay the transport of individual sheets in order to provide additional time for downstream processing to be performed. Such temporary holding or delaying of sheets is generally referred to as “buffering” and has been accomplished in many different ways. One method of buffering has been to temporarily slow or stop a roll nip or other paper transport for a period of time equal to the inter-copy-gap between successive sheets. If longer times are required, other systems may be used. For example, multi-sheet buffers have been developed to allow several sheets to accumulate. However, such buffers do not accommodate uncertainties in the timing of a marking engine.